FISH PRODUCTION IN THE WARTA RIVER - POSTIMPOUNDMENT STUDY

The mean biomass and production of fish populations in upstream and downstream sites of the Jeziorsko Reservoir (the Warta River, Central Poland), in four subsequent years after impoundment (1986-89), never reached values as high as those before impoundment. Despite considerable differences between the morphological characters of the two sites, similar changes in fish biomass and production were recorded. The lowest values, recorded in 1987 and 1988, were most probably dependent on a decline in water quality and on the abiotic factors accompanying dam construction (bank modification, removal of riparian vegetation, increased sediment load, short-term effect of releasing large volumes of water).